Single small coating spots/faults are common and may be due to a speck of dust on the glass before coating takes place.
Some high end lenses have to be coated immediately they are made (polished). If not the glass rapidly degrades. This is usually with exotic high refractive index glass, which is used in these optics costing $10,000 or more each.
It is the coating that protects the glass underneath.
I think that there are only two likely causes of the Nikon lens problem here. Coating fault or miniscule droplets.
Early 1960s and late 1950s Minolta and Canon lenses had great problems with grease volatilising and coating the iris blades. These lenses usually had seized up irises, which had to be cleaned, Lenses were simpler then and more easily dismantled. By the late 1960s these problems were solved with new greases.
I think that all TTH professional lenses were made with disassembly and cleaning in mind.
I was given a Zeiss 75cm f/6.3 Telikon lens that was sitting in English's optics skip in Essex. It had almost the whole front element deeply gouged out by metal girders in the skip.
On testing visually with an eyepiece I was amazed to see the original superb Zeiss quality show through, but with terrible loss of contrast. These were survey lenses of the highest quality for 30cm square format.
If the Nikon binocular looks good with normal use, then it isn't worth spending money on it.
Although I would probably not use it except as a car back up binocular just for emotional reasons rather than logic.
